High temperature vulcanizing silicone rubber (HTV-SR), such as high temperature vulcanized polydimethylsiloxanes (HTV-PDMS), are widely used in the electrical engineering industry, such as for outdoor insulation, due to their surface properties and the capability to recover hydrophobicity.
However, in outdoor and wet environment often erosion, patterns are observed on the rubber surface, whereby the electrical conductivity within the pattern can be considerably increased due to discharge degradation. The electrically conductive path has been referenced as a track, or as tracking. Tracks reduce the insulation strength and may lead to flashover or dielectric breakdown.
As a result, tracking-resistant polymer systems have been developed for the use as outdoor high-voltage insulation. One example is high temperature vulcanized polydimethylsiloxane (HTV-PDMS) filled with alumina trihydrate [(ATH), (Al2O3.3H2O)] containing, for example, about 30 to 70% by weight of ATH, calculated to the total weight of the insulation material [or 43 parts (phr) to 230 parts (phr) of ATH per 100 part of SR]. Such a material has been used to produce outdoor high-voltage insulation systems. Aluminium hydroxide [Al(OH)3] has been referred to as alumina trihydrate (ATH) because chemically (Al2O3.3H2O) corresponds to 2[Al(OH)3] but the term “ATH” has been used in the field of polymeric outdoor insulation.
Testing the tracking resistance of various commercial high temperature vulcanized silicone rubber (HTV-SR) and various commercial high temperature vulcanized polydimethylsiloxane (HTV-PDMS) according to IEC (International Electrotechnical Commission) standard 60587 at 4.5 kV revealed that these materials can fail during testing, showing deep erosion and a layer-wise degradation, resulting in a dielectric breakdown in the IEC 60587 tracking test. The degradation mechanism was found to be complicated, as temperatures of above 1200° C. (>1200° C.) and even higher than 1600° C. (>1600° C.) may arise during surface discharge. Therefore, the tracking and erosion resistance of filler containing HTV-SR can be further addressed.